When a shaft 5 shown in FIG. 9 is to be coupled to a member 1 having a circular shape or another shape, for example, the following structure may be employed. As shown in the figure, an end part of the shaft 5 is fitted into a cylindrical boss 2 which is formed integrally with the member 1, and the end face of the shaft 5 abuts against an inner flange 3 formed in the root part of the boss 2. A bolt 7 which is passed through a bolt through hole 4 formed by the inner flange 3 is screwed into a thread hole 6 formed in the shaft 5 to be fastened thereto. For example, this structure can be employed in the case where the member 1 is used for coupling the shaft 5 serving as a rotating shaft to a pulley of a rotation transmission mechanism such as a pulley disposed in a power steering system of an automobile or that used in usual industrial equipment.
When the member 1 shown in FIG. 9 is to be made of metal, the boss 2 and the inner flange 3 are usually formed by casting the member 1.
On the other hand, as a ring member such as a pulley and various kinds of gears, a sheet metal member which is produced by conducting a rolling process or a punching process on a flat sheet metal is used in order to reduce the weight of the ring member, enhance the toughness of the ring member, and lower the cost.
However, a ring member such as the member 1 shown in FIG. 9 in which the boss 2 has the inner flange 3 cannot be formed from a sheet metal because of a problem in production technique.